The conversion of anthracycline antibiotics as examplified by daunorubicin to 7-deoxyaglycone metabolites occurs via a protonated free radical anion intermediate. Intact daunosamine is the leaving group. Mitomycin C a quinone anticancer antibiotic in gastrointestinal tumors, is metabolized to a free radical by NADPH cytochrome P-450 reductase and xanthine oxidase. Nine metabolites were resolved by reversed phase high performance liquid chromatography. Identification by mass spectrometry showed cis and trans 2,7 diamino-1-hydroxymitosene were formed. Besides the reactive center at C1 following bioreduction, a second reactive center at C7 is implicated by these results.